1. Field of the Invention
This invention relates in general to devices for centering audio records on the platter of the turntables and in particular to devices for correcting the audio record's groove eccentricity.
2. Description of the Prior Art
The most common imperfection in audio discs is groove eccentricity. This kind of imperfection is caused mainly by three factors: (1) eccentric location of the record's central hole in relation to the record grooves, (2) oversized diameter of audio record's central hole, (3) undersized diameter of turntable's spindle shaft. It is apparent that these three factors can work against each other and add to each other's individual error. International standards require a maximum eccentricity error of 0.2 millimeters in audio records. However, the aggregate of the above mentioned factors can lead to an eccentricity error much higher than the above mentioned allowable eccentricity error of the record itself.
This type of eccentricity can cause distortion known as wow and flutter. The amount of the distortion produced by an eccentric record is significant. As a general rule, a doubling of a disc's eccentricity error leads to a doubling of wow and flutter in the reproduced sound. Even if all components of the record playing system are of high quality the distortions produced by an eccentric record cannot be overcomed and can significantly affect the quality of the sound reproduction. Accordingly, the results of a well-centered record are: reduced wow and flutter, reduced surface noise, improved frequency response, improved dynamic range, and improved stereo separation. The overall sonic improvement can be described as: added clarity and focusing of the sound, increased detailing, and stablized positioning of musical instruments and vocals in space.
Furthermore, in the ordinary procedures for centering a record on the turntable the record comes into physical contact with the turntable's spindle. This causes the vibrations of the moving parts of the turntable to be transmitted through the spindle shaft to the record and then picked up by the phono cartridge in form of noises and distortions. With respect to this problem another proposal provides a turntable with accoustic damping means to be positioned between the spindle pin and the spindle hole of the record in order to accoustically isolate the recording disc from the turntable's drive shaft. However, in this invention since the contact between the record and the spindle is not eliminated the vibrations transmitted to the record are merely reduced by the accoustic damping material and not totally eliminated. Furthermore, this proposal requires a turntable to be already built with this type of spindle means and cannot solve the problem for millions of turntables already made with a metal spindle shaft. On the other hand, using the object of my invention for centering a record and slightly enlarging the record's spindle hole the contact between the spindle and the record can be totally avoided and thereby the vibrations ordinarily transmitted to the record through the spindle shaft totally eliminated. Furthermore, my centering device and procedure can be employed for all turntables already in use without any changes or modifications in the turntable's components.